The present invention relates to a method for monitoring the functionality of the heating of a catalytic converter situated in an exhaust system of an internal combustion engine.
There are functions for catalytic converter heating in the engine controller for exhaust gas post-treatment, in particular for rapidly starting the catalytic converter or for rapidly reaching the light-off temperature. One of these functions is retarding the ignition angle and thus changing the combustion temperature in the exhaust system. The reduction of the untreated emission also accompanies this—A further secondary condition is that the efficiency decreases by the shift because of which a load increase occurs. This load increase is an increase of the mass throughput which comes through the catalytic converter. Such a combination of the ignition angle retarding and the increase of the mass throughput causes a temperature increase and an exhaust gas post-treatment. The ignition angle shift is performed in a modern engine controller (which is torque-guided) on the basis of a torque model, as described, for example, in German Patent Document DE 101 49 477 A1.
Various methods for monitoring and controlling such catalytic converter heating measures are known. In addition, the California Air Resources Board (CARB) encourages the diagnosis of the ignition angle intervention, which is also responsible for the heating of the catalytic converter, in the scope of the topic of “cold start monitoring.” Without this function, licensing is made significantly more difficult. Up to this point, there has been no monitoring of the actual ignition angle intervention for the rapid heating of the catalytic converter. Only the indirect variables which result in the setting of the ignition angle in the catalytic converter heating mode, such as the throttle valve, the idle speed, the air-mass meter, and the ignition system, are currently monitored.
The present invention therefore specifies a method for monitoring the functionality of the heating of a catalytic converter situated in an exhaust system of an internal combustion engine, which is based on monitoring the ignition angle intervention.
According to the present invention, there is described a method for monitoring the functionality of the heating of a catalytic converter situated in an exhaust system of an internal combustion engine, in which a current ignition angle is acquired over a specified time and converted into a torque model used for catalytic converter heating, using which a degree of fulfillment of executed catalytic converter heating measures is obtained, through which an error signal is generated using a limiting value comparison.
A method of this type connects the official requirement for ignition angle monitoring to the torque model used for the catalytic converter heating. The function is thus more resistant to errors than solely monitoring the ignition angle. Because it is a purely diagnostic method, no change in the driving behavior is to be expected and thus no reapplication/monitoring are necessary, as in ignition angle limiting.
To convert the current ignition angle into the torque model from a current ignition angle, the ACTUAL torque reserve is advantageously determined by calculating an intake air mass and an ignition angle efficiency, the ignition angle efficiency being obtained in that the current ignition angle is compared to an optimal ignition angle for the current operating point. A reference torque results from the intake air mass here.
The degree of fulfillment of executed catalytic converter heating measures is preferably obtained by comparing the ACTUAL torque reserve determined from a current ignition angle to a SETPOINT torque reserve, corresponding thereto, requested for the catalytic converter heating measures.
In this case, the degree of fulfillment of the executed catalytic converter heating measures is further preferably obtained in that differences of ACTUAL torque reserves, determined from a current ignition angle, to SETPOINT torque reserves corresponding thereto are summed over the specified time and the summed differences are compared to the corresponding summed SETPOINT torque reserves. The summation of the differences of ACTUAL torque reserves determined over the specific time from a current ignition angle to SETPOINT torque reserves corresponding thereto and the summation of the SETPOINT torque reserves preferably is performed in each case via integration.
Furthermore, the comparison of the summed differences to the correspondingly summed SETPOINT torque reserves preferably is performed via a quotient calculation. In this case, a percent deviation of the ACTUAL torque reserves from the SETPOINT torque reserves requested for the catalytic converter heating measures may be acquired especially easily.
According to the present invention, an error is preferably indicated by the error signal if the degree of fulfillment of executed catalytic converter heating measures lies below a predetermined limiting value. The generated error signal may, for example, cause an entry of the error “catalytic converter heating faulty” in an error memory of the vehicle.
According to the present invention, the specified time is preferably defined via a predetermined sum of summed SETPOINT torque reserves requested for the catalytic converter heating measures. In this way, it is taken into consideration that the detection of an error is more reliable after a minimal time span, because of which an error is first output when a certain summed SETPOINT catalytic converter heating torque reserve, i.e., a total SETPOINT torque reserve, is reached.
An error indicated by the error signal is advantageously debounced in an error memory manager according to the present invention. In this way, the error may be digitally debounced in an especially simple way, without the actual monitored signal of the ignition angle intervention having to be debounced.
The monitoring according to the present invention of the functionality of the heating of a catalytic converter situated in an exhaust system of an internal combustion engine is preferably performed when the internal combustion engine is in an idle state. To ensure that otherwise no such functionality check will occur, zero values are preferably applied within the diagnostic unit to the integrators for summing the differences of ACTUAL torque reserves determined over the specified time from a current ignition angle, to SETPOINT torque reserves corresponding thereto and the SETPOINT torque reserves.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.